Re: [Xen-devel] [PATCH v2] xen: Implement hypercall for tracing of program counters

[Julien Grall <julien.grall@xxxxxxx>]

On 31/07/17 10:56, Wei Liu wrote:
> On Mon, Jul 31, 2017 at 09:22:35AM +0100, Julien Grall wrote:
> > Hi,
> >
> > On 07/28/2017 04:37 PM, Wei Liu wrote:
> > > On Wed, Jul 26, 2017 at 12:43:45PM +0200, Felix Schmoll wrote:
> > > > +        d->tracing_buffer = NULL;
> > > > +
> > > > +        if ( copy_to_guest(buf, temp, d->tracing_buffer_pos) )
> > > > +            ret = -EFAULT;
> > > > +
> > > > +        xfree(temp);
> > > > +
> > > > +        ret = d->tracing_buffer_pos;
> > > > +        break;
> > > > +    }
> > > > +
> > > > +    default:
> > > > +        ret = -ENOSYS;
> > > EINVAL
> > Should not it be -EOPNOTSUPP to match return error when CONFIG_TRACE_PC is
> > not?
> AIUI EOPNOTSUPP means "This is a valid operation but I am not configured
> to support it" while EINVAL means "This is an invalid value
> (operation)".
Fair enough. However, you impose the caller to check -EINVAL and 
-EOPNOTSUPP in order to know if an operation can be done.
I first thought all the other hypercalls use -EOPNOTSUPP, but in face 
they use -ENOSYS. It would be to be consistent with the rest rather than 
reinventing our own.
--
Julien Grall

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